JPH074019B2 - Method and device for automatic white balance adjustment - Google Patents

Description

The present invention relates to an automatic white balance adjusting method and device, and more particularly to an automatic white balance adjusting method and device for automatically adjusting white balance by an internal photometric method.

[Conventional technology]

Conventionally, there are an external photometry method and an internal photometry method as the automatic white balance adjustment method. In the external photometry method, the color temperature is measured by an external sensor and the red / red
This is so-called open-loop control that controls the gain of the blue signal. In such a system, if the color temperature of the light hitting the subject and the color temperature of the light entering the external sensor are different, an error occurs and the color tone becomes unnatural. For example, when taking a picture of the outdoors through a window from an illuminated room, the external sensor is exposed to light with a low color temperature in the room, so control that makes the color tone blue is applied, and It becomes a strong image.

On the other hand, in the internal photometry method, the color is appropriate because the light that hits the subject is directly determined.

The conventional automatic white balance adjusting method of the internal photometry will be described with reference to FIG. 6. The light incident through the lens 10 passes through the image sensor 12 to generate red, green and blue signals (E _R , E). _G ,
It is photoelectrically converted into E _B ). Each signal _{(E R, E G, E} B) is input to a matrix circuit 20 via the amplifier 14, 16, 18, respectively, wherein the luminance signal E _Y and the color difference signal _{(E R -E Y), (} E _B-
After being converted into E _Y ), it is input to the encoder 22. In the encoder 22, the color difference signals are so-called 3.58MHz and orthogonal 2
The signal is phase-modulated, added to the luminance signal E _Y, and output as an NTSC video signal.

On the other hand, the color difference signals (E _R -E _Y ) and (E _B -E _Y ) are input to the integrating circuits 24 and 26, respectively, where the color difference signals of the entire screen are integrated, and the integrated average value is the difference. Motion amplifiers 28 and 30
Is added to the negative input of. To the positive inputs of the differential amplifiers 28 and 30, the color difference signals (E _R -E _Y ) and (E _B -E _Y ) when the average value of the colors of the entire screen becomes gray from the reference level setters 32 and 34, respectively. ) Is inputted, the differential amplifier 28 outputs the gain control signal R _CONT obtained by amplifying the difference between the two input signals to the amplifier 14 and amplified by the amplifier 14. that controls the gain of the signal E _R, also the differential amplifier 30 outputs a gain control signal B _CONT obtained by amplifying the difference between the two input signals to the amplifier 18, the signal E _B to be amplified by the amplifier 18 Control the gain. This gives the signals E _R and E _B
The average value of the color difference signals (E _R -E _Y ) and (E _B -E _Y ) on the entire screen is controlled so as to match the reference level.

That is, the automatic white balance adjustment method described above is gray when the colors of the entire colored screen are averaged (equivalent to shooting a white subject when averaging the entire screen even when shooting a general subject). It becomes a control method based on the general fact.

[Problems to be solved by the invention]

However, not all subjects satisfy the above assumptions. For example, for subjects with a background of blue sky and blue sea, or subjects with a background of red walls, integrating (averaging) the entire screen will result in blue or red. And not gray. When the white balance adjustment is performed on such a subject, both blue and red become gray, and erroneous control called so-called color failure is performed.

The present invention has been made in view of such circumstances, and an object thereof is to provide an internal photometric automatic white balance adjusting method and apparatus capable of eliminating or minimizing erroneous control of color ferria.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention uses color difference signals (E _R -E _Y ) and (E _B -E _Y ) from signals obtained by photographing a subject, respectively.
In the automatic white balance adjusting method, each color difference signal is integrated over the entire screen, and the gains of the red and blue signals are controlled so that each integrated average value becomes a predetermined reference level. For each color difference signal, the slice level for removing the strong color difference is set, and for the strong color difference signal exceeding the set slice level among the color difference signals, the slice level is integrated instead of the strong color difference signal, and The feature is that the super color difference signal is removed from the color difference signal.

[Action]

According to the present invention, when the color difference signals (E _R -E _Y ) and (E _B -E _Y ) generated from the signal obtained by photographing the subject are integrated to obtain the average value of the entire screen, Color difference signals (super color difference signals) above a certain level (slice level) are not integrated,
Instead of the super color difference signal, the slice level is integrated. That is, even if the average of the entire screen of the original picture is not gray, the information obtained by removing the strong color from the original picture is integrated to bring it closer to gray, thereby eliminating the erroneous control of the color ferria.

〔Example〕

Hereinafter, preferred embodiments of an automatic white balance adjusting method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

First, the present invention will be described in principle with reference to FIG.

Now, it is assumed that the color difference signal (E _R -E _Y ) shown in FIG. 2 (B) is obtained from a pattern including a strong red color as shown in FIG. 2 (A). When this color difference signal is integrated over the entire screen,
When the integrated average value moves to the red side from the black level and the automatic white balance adjustment as shown in FIG. 6 is performed,
The color of the human face is erroneously controlled in the complementary color direction of red (cyan, blue).

Therefore, a certain level (slice level) is set in order to slice the color difference signal indicating strong red from the pattern of FIG. 2 (A), and the strong color difference signal exceeding this slice level is shown in FIG. 2 (C). Set to slice level as shown. As a result, the strong color difference signal is removed from the color difference signal of the original pattern, and the average value becomes closer to gray.

FIG. 1 is a block diagram showing an embodiment of an automatic white balance adjusting device according to the present invention. The same parts as those in FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted.

As is clear from FIG. 1, a portion (amplitude limiting section) 40 shown by a chain double-dashed line is a portion added by the present invention, and the amplitude limiting section 40 limits the amplitude of the above-mentioned super color difference signal. I am trying.

The amplitude limiting section 40 includes an upper limit limiter 41 including an upper bias power supply section 41A and a diode 41B for a color difference signal (E _R -E _Y ), a lower limit limiter 42 including a lower bias power supply section 42A and a diode 42B, and a color difference signal (E _B -E _Y ) Upper limit limiter 43 consisting of upper bias power supply 43A and diode 43B, lower bias power supply 4
It consists of a lower limiter 44 consisting of 4A and a diode 44B.

The upper bias power supply unit 41A and the lower bias power supply unit 42A respectively set an upper slice level and a lower slice level for slicing the red-side strong color difference signal and the cyan-side strong color difference signal of the color difference signal (E _R -E _Y ), respectively. To set, and also
The upper bias power supply unit 43A and the lower bias power supply unit 44A respectively set the upper slice level and the lower slice level for slicing the blue-side strong color difference signal and the yellow-side strong color difference signal of the color difference signal (E _B -E _Y ), respectively. It is something to set.

Therefore, the amplitude value of the super color difference signal exceeding the upper slice level or the lower slice level is limited to the upper slice level or the lower slice level by the upper limiter or the lower limiter. For example, the bias voltage by the bias power supply unit 41 of the upper limiter 41 is E ₁ , the bias voltage by the bias power supply unit 42A of the lower limiter 42 is E _2, and the third
When a color difference signal (E _R -E _Y ) as shown in FIG. 3A is input, the upper limit limiter 41 and the lower limit limiter 42 limit the color difference signal as shown in FIG. Will be output to 24.

As a result, even if the original picture partially contains strong colors, the average of the colors obtained by subtracting the strong colors from the picture is taken, and the average can be made closer to gray, affecting the strong colors. You can adjust the white balance properly.

Next, a case where the slice level is automatically set to an appropriate value will be described.

That is, FIGS. 5A and 5B show the same picture and color difference signal (E _R -E _Y ) as in FIGS. 2A and 2B, but the color temperature is different for this picture. Change, the color difference signal (E _R -E _Y ) changes so that the DC offset moves up and down with respect to the black level while maintaining the original waveform as shown in FIG. 5 (C). Here, when the same slice level as that in FIG. 5B is set, the non-sliced portion (hatched portion) A in FIG. 4C is erroneously detected as a strong color difference signal and is sliced. .

Therefore, as shown in FIG. 5 (D), if the slice level is also increased by the amount (ΔV) that the average value has increased due to the change in color temperature, only the strong red color at the same position as in FIG. 5 (B). Can be detected and sliced.

FIG. 4 is a block diagram of essential parts showing another embodiment of the automatic white balance adjusting apparatus according to the present invention, in which the slice level is automatically set to an appropriate value.

In the figure, the color difference signals (E _R -E _Y ) and (E _B -E _Y ) are applied to clamp circuits 54 and 56 via amplifiers 50 and 52, respectively. A clamp pulse CP is applied to each of the clamp circuits 54 and 56, and each of the clamp circuits 54 and 56 applies a color difference signal (E _R -E _Y ) and (E _B -E _Y ) to the clamp pulse CP.
The pedestal clamp is synchronized with.

The color difference signal (E _R -E _Y ) pedestal clamped by the clamp circuit 54 is applied to the integrating circuit 24 via the buffer 58, the amplitude limiting section 60 and the buffer 66, and is also applied to the integrating circuit 68. The integrating circuit 68 integrates the input color difference signal (E _R -E _Y ) and stores the integrated average value of the entire screen in the buffer 6
It is added to the amplitude limiting unit 60 via 9.

The amplitude limiting unit 60 includes an upper bias power supply unit 62A and a diode 6
The upper bias power supply unit 62A is composed of an upper limit limiter 62 composed of 2B and a lower limit power supply unit 64A and a lower limit limiter 64 composed of a diode 64B. A voltage (upper slice level) is applied in the reverse direction of the diode 62B, and the lower bias power supply unit 64A applies a bias voltage (lower slice level) smaller than the integrated average value applied from the integrating circuit 68 by a fixed level in the forward direction of the diode 64B. Is being applied to. Therefore, the upper slice level and the lower slice level fluctuate according to the integrated average value added from the integrating circuit 68.

Then, the color difference signal (E _R-
A signal of E _Y ) that exceeds the upper slice level or the lower slice level has its amplitude value limited to the upper slice level or the lower slice level and is output to the integrating circuit 24 in the subsequent stage.

Similarly, the color difference signal (E _B -E _Y ) pedestal clamped by the clamp circuit 56 is stored in the buffer 72 and the amplitude limiter 74.
And to the integrating circuit 26 via the buffer 76, and to the integrating circuit 78. The integrating circuit 78 integrates the input color difference signal (E _B −E _Y ) and adds the integrated average value of the entire screen to the amplitude limiting unit 74 via the buffer 79. The amplitude limiting unit 74 has the same configuration as the amplitude limiting unit 60 described above,
Also, based on the integrated values of the integration circuits 24 and 26, the gain limit signal
Since the circuit for generating R _CONT and B _CONT is the same as that of FIG. 6, its explanation is omitted here.

〔The invention's effect〕

As described above, according to the automatic white balance adjusting method and device of the present invention, when there is a strong color (color with a high degree of saturation) in the design, the size of the color is limited to a predetermined slice level. Since it is made to average, the average value of the color of the entire screen can be brought close to gray, and the false control of the color ferria can be eliminated or minimized.
Good white balance adjustment is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic white balance adjusting device according to the present invention, and FIGS. 2 (A) to (C) are diagrams used for explaining the principle of the present invention, and FIG. (A) and (B) are waveform charts used for explaining FIG. 1, FIG. 4 is a block diagram of essential parts showing another embodiment of the automatic white balance adjusting apparatus according to the present invention, and FIG. A) to (D) are diagrams used for explaining a preferable method of setting the slice level, and FIG. 6 is a block diagram showing an example of a conventional automatic white balance adjusting device. 10 ... Lens, 12 ... Image sensor, 14, 16, 18 ... Amplifier, 20 ... Matrix circuit, 22 ... Encoder, 24, 2
6, 68, 78 …… Integrator circuit, 28,30 …… Differential amplifier, 32,3
4 …… Reference level setter, 40, 60, 74 …… Amplitude limiter, 4
1, 43, 62 …… Upper limiter, 42, 44, 64 …… Lower limiter.

Claims (2)

[Claims] 1. Color difference signals (E _R -E _Y ) and (E _B -E _Y ) are generated from signals obtained by photographing a subject, and the respective color difference signals are integrated over the entire screen, and respective integrated averages are obtained. In the automatic white balance adjusting method for controlling the gains of the red and blue signals so that the values are respectively predetermined reference levels, the color difference signals are integrated over the entire screen,
A level above and below the integrated average value by a certain level with respect to each integrated average value is set as a slice level for supercolor difference removal for each color difference signal, and the set slice level of each color difference signal is set. An automatic white balance adjusting method characterized in that, for a strong color difference signal that exceeds, the slice level is integrated instead of the strong color difference signal, and the strong color difference signal is removed from each color difference signal. 2. A first gain control circuit and a second gain control circuit for controlling the gains of red and blue signals of a signal obtained by photographing a subject, respectively, and signals generated by photographing the subject. The color difference signals (E _R -E _Y ) and (E _B -E _Y ) are respectively input, and the first and second integrating circuits for respectively integrating the color difference signals over the entire screen are included. First and second slice level setting means for setting an upper slice level larger by a constant level and a lower slice level smaller by a constant level than the integrated average value of the integrating circuit as a reference; The color difference signals (E _R -E _Y ) and (E _B -E _Y ) generated from the signals obtained by photographing are input, respectively, and the upper slice level set by the first and second slice level setting means is set. Larger color difference signal and below First and second amplitude limiting circuit having a small color difference signals than Rice level to limit the amplitude of the color difference signal so as not outputted, the first color difference signal through the second amplitude limiting circuit (E _R - E
_Y ) and (E _B -E _Y ) are integrated over the entire screen, respectively, and third and fourth integrator circuits, and first and first are set as predetermined reference levels to be taken by the average value of each color difference signal over the entire screen. The reference level setter of No. 2 and the integrated average value of the third integrator circuit are compared with the reference level of the first reference level setter, and the gain of the first gain control circuit is adjusted so that they match. Means for adjusting, and means for comparing the integrated average value of the fourth integrator circuit with the reference level of the second reference level setter, and adjusting the gain of the second gain control circuit so that they match. And an automatic white balance adjusting device.